1. Field of the Invention
This invention relates generally to a powertrain for a hybrid electric vehicle and, in particular, to detecting the start of sustained combustion in an internal combustion engine (ICE).
2. Description of the Prior Art
In a vehicle powertrain where a starter/generator has a continuous drive connection to an engine and a selective connection to a transmission through an input clutch whose torque capacity is variable, the vehicle is frequently driven solely by the starter/generator without the engine operating. The engine is frequently stopped to prevent use of engine fuel and is frequently restarted when engine torque is required to augment power produce by the starter/generator.
Detecting that an internal combustion engine has been successfully started is confirmed upon observing stable, sustained combustion in the engine's combustion chamber. A reliable technique for determining that the engine has been started or restarted is required in a powertrain of this type.
It is conventional to start an engine in a vehicle powertrain in which the starter/generator does not have a full time connection to the engine. In such cases, the starter electric motor is connected to the engine by a one-way torque transmitting device, a one-way clutch, such that the starter motor can only add torque to the engine, and the engine is permitted to rotate freely faster than the starter motor speed. In such configurations, engine start detection criteria consists of considering the engine speed relative to the idle reference and/or the starter motor speed over some period of time. An engine speed threshold condition and a duration threshold are used.
A speed based engine start detection scheme is not reliable is a powertrain having of the full-time connection between the engine and the electric machine that starts the engine. Any torque disturbance resulting from an engine start is difficult to observe in the speed domain because the electric machines are continually connected to the engine and the speed reference is regulated by the electric machine. Engine speed cannot exceed the starter/generator speed.
Furthermore, aggressively close engine start and transmission events can distort engine start detection mechanism when there is overlap of transmission events during the engine start process when using conventional start detection techniques.